1. Field of the Invention
The present invention relates to a nano-carbon fiber and a method for preparing the same. The nano-carbon fiber of the present invention is used for an electronic device, an electrode of a secondary battery or fuel battery, hydrogen absorbing material, composite material and electromagnetic wave absorber.
2. Discussion of Background
Almost all of the conventional carbon nano-fibers (carbon superfine fiber) are straight fibers such as VGCF (vapor growth carbon fiber), carbon nano-tube, etc. A carbon microcoil having a fiber diameter in the order of micrometer or a carbon nano-coil having a fiber diameter finer than that of the former has been known as a spiral carbon fiber. Such spiral carbon fibers are produced by the use of a catalyst. Particularly, a carbon nano-coil is produced by the use of Fe.In.Sn mixed catalyst or mixed catalyst of oxide thereof (Unexamined Japanese Patent Publication (Kokai) No. 2001-192204) or Ni catalyst carried on Cu substrate (Unexamined Japanese Patent Publication (Kokai) No. 2001-240403).
It is expected that a carbon fiber is applied to wide variety of uses, for example, an electronic device such as an electron emission source, a display tube, a display panel, an emission display, an emission tube, an emission panel, etc. using the electron emission source, an electrode for a secondary battery or fuel battery, a hydrogen absorbing material, an electromagnetic wave absorber, additives to be added into rubber, plastics, resin, metal, ceramic, concrete, etc. for improving functions such as mechanical strength, color, electrical conductivity, thermal conductivity, etc. A mixture of a carbon fiber with rubber, plastics, resin, metal, ceramic or concrete, etc. is called “composite” or “composite material.”
Above all, a spiral or twisted carbon fiber shows various properties which a straight carbon fiber does not possess. For example, the spiral or twisted carbon fiber has a large surface area compared with a straight carbon fiber having the same length of fiber, has a fine curved surface or angle as seen from any direction, has an electrical inductance, and has a mechanical spring function.
Therefore, a development of application is possible by using such characteristics. When a spiral or twisted carbon fiber is applied to the above-described applications, a method has been required for preparing such a carbon fiber effectively and in high volumes, and a technology for controlling the shape thereof has been required.
Unfortunately, however, there has not been proposed a mass-production and controlling method of a carbon fine fiber such as spiral (coil-shaped) or twisted carbon fiber having a fiber diameter of 1 μm and below.